What is the main conflict in Mind Prey by John Sandford?

In Mind Prey, Lucas is called in on a kidnapping case involving the daughter of wealthy businessman Tower Manette. Lucas begins the case focusing on greed as a motive, but begins to believe a patient of psychologist Andi Manette may behind the kidnapping. This instinct seems to be confirmed when Mail begins calling Lucas, giving him cryptic hints to the well being and location of Andi and her daughters.